[CQ-Contest] SDR Mythbusters - ADC Overload myths debunked...

[Marijan Miletic]

K9YC wrote:

 

>The Noise Power Ratio Test is especially problematic -- the level of the
test signal is not a constant, but is adjusted to depend on characteristics
of the radio being tested. 

 

HF is noisy and overcrowded by powerful broadcasting signals and
over_the_horizon radars.  Semiconductors are used these days so there is no
problem receiving signals slightly above the fixed thermal noise level.  We
fight overloading with antenna attenuators and old RX test results show that
gain change with constant test signal.

 

 

>Thus, SDRs with limited dynamic range are tested at lower signal levels.
The results cannot be compared to other radios -- it's apples and oranges. 

 

Good RX these days is statistically better in extracting single signal from
the mess of others and NPR test is just that!  SDR math does that better
than analog filtering with a single clean oscillator doing ADC for the whole
bandwidth.  The only problem might be long term ADC overflow in the case of
collocated TX (military ships, ham M/M). 

 

>Truly objective engineers familiar with his work have blown huge holes in
it, and others have noted that he acts as a mouthpiece for ICOM. 

 

Could you give us any reference?  AB7OJ tested all manufacturers radios and
just found IC-7851 to be the best.  I am glad for IC-7300 SDR DDC coming so
we are both Icom salesman?  

 

>I heard Adam speak and later had dinner with him a few months ago. Nice
guy, retired from the RF side of telco, but either biased or sees the world
through blinders. 

 

Einstein didn't see the world thru Newton blinders!  Motorola Tayloe gave us
elegant IQ digital mixer initially used by K5SDR.  Even Canada is going for
CHANGE!

 

73 de Mario, S56A, N1YU, MSc EE retired